EVALUATION OF WEED-CONTROL PRACTICES DURING SPRING AND SUMMER ALFALFA ESTABLISHMENT

Weed management during alfalfa (Medicago sativa L.) establishment is a major concern for producers in the northeast USA. The objectives of this research were to determine the yield, quality, and economic consequences of controlling weeds during the establishment of spring- and summer-seeded alfalfa. Alfalfa was band-seeded during spring (April and May) and late summer (August and September) into a conventionally tilled seedbed of Hagerstown silt loam (fine-loamy, mixed, mesic Typic Hapludalfs) at Landisville, PA, in 1991 and Murrill silt loam (fine-loamy, mixed, mesic Typic Hapludult) at Rock Springs, PA, in 1991 and 1992. Weed control treatments for the spring seedings included: (i) no herbicide or nurse crop (no weed control); (ii) oat (Avena sativa L.) nurse crop; (iii) benefin preplant incorporated; and (iv) sethoxydim and 2,4-DB postemergence. Weed control treatments for late-summer seedings were the same as those in the spring except that the nurse crop was replaced with a paraquat application to dormant alfalfa. Seeding alfalfa later, compared with earlier, in the spring tended to increase weed and decrease alfalfa dry matter (DM) yield but did not affect total DM yield or forage quality during the seeding year. For spring-seeded alfalfa, weed control treatment effects on alfalfa and weed DM yield during the seeding-year were sporadic, however, net economic return per acre was generally greatest when no weed control was used. Neither time of spring seeding nor weed control treatments produced consistent differences in yield, quality, or net economic return per acre after the seeding year. Delaying alfalfa seeding in the summer reduced first harvest alfalfa yield (704 lb/acre less) and season total alfalfa yield (1121 lb/acre less) compared with early seedings. Generally, weed control treatments in summer-seeded alfalfa did not improve alfalfa or total DM yield, forage quality, or net economic return per acre compared with no weed control. We conclude that when alfalfa is either spring or summer seeded, the weed control practices used in this study were not economically beneficial and may actually reduce net return per acre because of associated additional costs compared with seeding alfalfa with no companion crop or herbicide.